[Gbbopen-list] deleted-unit-instance

[Dan Corkill]

One additional note:

In addition to deleting a unit instance (and using the new
DELETED-INSTANCE-CLASS functionality), there is always the option of using
CHANGE-CLASS rather than DELETE-INSTANCE.  Changing the class of a unit
instance to a class that is a non-unit-instance (not a subclass of
STANDARD-UNIT-INSTANCE) has the side-effect of removing the unit instance
from the blackboard repository.

I think that the new DELETE-INSTANCE functionality is probably clearer when
the intent is to actually delete the unit instance (and not access it any
longer--except for debugging purposes).  On the other hand, using
CHANGE-CLASS to change a unit instance into a non-unit-instance is probably
clearer as to intent when the objective is to continue to use the
object--but no longer have it be a unit instance (and thus also have it
removed from the blackboard repository).  Another difference between the
DELETE-INSTANCE versus CHANGE-CLASS choice is the event functions that are
triggered in each case.

As always, increased flexibility brings additional programming-style
decisions...!

-- Dan





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